This invention relates to the manufacture of irrigation hose and, more particularly, to a high speed method and apparatus for forming inlet and/or outlet ports in drip irrigation hose.
One highly successful type of drip irrigation hose for use on row crops is made from an elongated plastic film and extruded plastic beads. The plastic film is folded to overlap its longitudinal margins to form a water supply passage. Two longitudinal side by side plastic beads interconnect the overlapping margins to define along their length a flow regulating passage. At regular intervals, a passage blocking cross bead is formed between the beads to divide the flow regulating passage into discrete segments. One or more inlet ports at one end of each segment couples the water supply passage to the flow regulating passage, and one or more outlet ports at the other end of each segment couples the flow regulating passage to the exterior of the hose.
The inlet and outlet ports are either created in the beads or in the film. In beads, the ports are formed by a molding wheel. In film, the ports are formed by various techniques, including a laser, a slit forming knife, a sharp edged, reciprocating hole punch that is driven against a rigid film backing surface or a reciprocating punch and die set.
Speed is an important consideration in the manufacture of drip irrigation hose. The rate of production is governed by the speed at which the manufacturing operations can be successfully performed. The currently known techniques for forming ports in the film are rather slow. Although the inlet and outlet ports can be formed in the beads by a molding wheel at high speed, this type of outlet port is particularly vulnerable to root intrusion, because roots tend to creep along the edge of the overlapping margins into the outlets. A root guard is sometimes used to prevent intrusion into the hose.